Calculating Depreciation

I am trying to create a table that calculates equipment depreciation by straight line, sum of years, and double-declining, because we have a number of different equipment types that depreciate in very different ways, but want to monitor all of them in one place.

I am struggling to find a way to calculate the accumulated depreciation in each given period. Straight line was no problem, but the sum of years is reminding me a lot too much of high school calculus and I’m ready to take it all back into an Excel sheet no one will ever look at again. I haven’t tried the double-declining yet, but I’m hoping it’ll be easy after sum of years!

Is this even possible in Airtable? I suspect I will need helper fields and don’t really want to go there in case some future equipment has a much longer lifespan than I’ve built in. Excel has an SYD function to get the period Depreciation Expenses, but nothing (that I’ve found) to give you the Accumulated Depreciation without referencing another row.